title: Riccardin D induces cell death by activation of apoptosis and autophagy in osteosarcoma cells.
abstract: Macrocyclic bisbibenzyls, characteristic components derived from liverworts, have various biological activities. Riccardin D (RD), a liverwort-derived naturally occurring macrocyclic bisbibenzyl, has been found to exert anticancer effects in multiple cancer cell types through apoptosis induction. However, the underlying mechanisms of such effects remain undefined. In addition, whether RD induces other forms of cell death such as autophagy is unknown. In this study, we found that the arrest of RD-caused U2OS (p53 wild) and Saos-2 (p53 null) cells in G1 phase was associated with the induction of p53 and p21(WAF1) in U2OS cells. RD-mediated cell cycle arrest was accompanied with apoptosis promotion as indicated by changes in nuclear morphology and expression of apoptosis-related proteins. Further studies revealed that the antiproliferation of RD was unaffected in the presence of p53 inhibitor but was partially reversed by a pan-inhibitor of caspases, suggesting that p53 was not required in RD-mediated apoptosis and that caspase-independent mechanisms were involved in RD-mediated cell death. Except for apoptosis, RD-induced autophagy occurred as evidenced by the accumulation of microtubule-associated protein-1 light chain-3B-II, formation of AVOs, punctate dots, and increased autophagic flux. Pharmacological blockade of autophagy activation markedly attenuated RD-mediated cell death. RD-induced cell death was significantly restored by the combination of autophagy and caspase inhibitors in osteosarcoma cells. Overall, our study revealed RD-induced caspase-dependent apoptosis and autophagy in cancer cells, as well as highlighted the importance of continued investigation on the use of RD as a potential anticancer candidate.
authors.affiliation: Department of Natural Product Chemistry, Key Lab of Chemical Biology of MOE (Ministry of Education), Shandong University, Jinan 250012, China.
authors.forename: Yanyan
authors.initials: Y
authors.lastname: Wang
authors.forename: Yuan
authors.initials: Y
authors.lastname: Ji
authors.forename: Zhongyi
authors.initials: Z
authors.lastname: Hu
authors.forename: Hanming
authors.initials: H
authors.lastname: Jiang
authors.forename: Fanghua
authors.initials: F
authors.lastname: Zhu
authors.forename: Huiqing
authors.initials: H
authors.lastname: Yuan
authors.forename: Hongxiang
authors.initials: H
authors.lastname: Lou
mesh_terms: D000972:Antineoplastic Agents, Phytogenic / Q000494:pharmacology*; D017209:Apoptosis / Q000187:drug effects; D001343:Autophagy / Q000187:drug effects; D002453:Cell Cycle / Q000187:drug effects; D045744:Cell Line, Tumor; D049109:Cell Proliferation / Q000187:drug effects; D002470:Cell Survival / Q000187:drug effects; D006801:Humans; D008869:Microtubule-Associated Proteins / Q000378:metabolism; D012516:Osteosarcoma / Q000378:metabolism; D010647:Phenyl Ethers / Q000494:pharmacology*; D013267:Stilbenes / Q000494:pharmacology*
chemical_list: D000972:Antineoplastic Agents, Phytogenic; C502070:MAP1LC3B protein, human; D008869:Microtubule-Associated Proteins; D010647:Phenyl Ethers; D013267:Stilbenes; C547185:riccardin D
keywords: Apoptosis; Autophagy; Cell cycle arrest; Riccardin D; p53